If the expected 'returnType' is 'null', just do not check it.

pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart

Index: pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
diff --git a/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart b/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
index dc011c1b0232b0b4ebbf0e0d7ce9f84a419dd37b..24b9aaa30be75b8914c5d1db3c2edae9f1628263 100644
--- a/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
+++ b/pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart
@@ -262,8 +262,6 @@ abstract class DartCompletionContributorTest extends AbstractContextTest {
       expect(cs.returnType, returnType);
     } else if (isNullExpectedReturnTypeConsideredDynamic) {
       expect(cs.returnType, 'dynamic');
-    } else {
-      expect(cs.returnType, isNull);
     }
     protocol.Element element = cs.element;
     expect(element, isNotNull);
@@ -278,8 +276,6 @@ abstract class DartCompletionContributorTest extends AbstractContextTest {
       expect(element.returnType, returnType);
     } else if (isNullExpectedReturnTypeConsideredDynamic) {
       expect(element.returnType, 'dynamic');
-    } else {
-      expect(element.returnType, isNull);
     }
     assertHasParameterInfo(cs);
     return cs;
@@ -419,8 +415,6 @@ abstract class DartCompletionContributorTest extends AbstractContextTest {
       expect(cs.returnType, returnType);
     } else if (isNullExpectedReturnTypeConsideredDynamic) {
       expect(cs.returnType, 'dynamic');
-    } else {
-      expect(cs.returnType, isNull);
     }
     protocol.Element element = cs.element;
     expect(element, isNotNull);
@@ -431,8 +425,6 @@ abstract class DartCompletionContributorTest extends AbstractContextTest {
       expect(element.returnType, returnType);
     } else if (isNullExpectedReturnTypeConsideredDynamic) {
       expect(element.returnType, 'dynamic');
-    } else {
-      expect(element.returnType, isNull);
     }
     assertHasNoParameterInfo(cs);
     return cs;